Pre-mRNA splicing is an integral step of eukaryotic gene expression. Splicing its regulation is important for cell survival, proliferation, development, and defects in splicing are associated with many genetic diseases. Although the basic mechanisms of splicing have been well characterized, little is known about how splicing is regulated by cell signaling. SRp38 is a general splicing repressor that is activated by dephosphorylation specifically in mitosis, and in response to heat shock and other cellular stress. This proposed study is to investigate the phosphorylation regulation of SRp38 by the cell cycle and the stress signaling pathways. Results of this study will not only reveal the role of phosphatases in regulating SR protein activity, but also enlighten us as to the general mechanisms by which cell signaling regulates splicing.